Because LED lamps possess advantages of energy saving, high efficiency, environmental protection and long life, they have been widely adopted in the lighting field. For LED lamps used as an energy-saving green light source, a problem of heat dissipation of high-power LED lamps becomes more and more important. Overheating will result in attenuation of lighting efficiency. If waste heat from working high-power LED lamps cannot be effectively dissipated, then the life of LED lamps will be directly negatively affected. As a result, in recent years, solution of the problem of heat dissipation of high-power LED lamps is an important issue for the industry.
In some applications, there may be a weight limit for a whole LED lamp. For example, when an LED lamp is provided with a lamp head with a specific specification and the LED lamp is used in a hanging manner, a maximum weight of the LED lamp is subject to a limited range. Accordingly, other than necessary components such as a power source, a lamp cover and a lamp shell, weight of a heat sink of an LED lamp is restricted to a limited range. For those high-power LED lamps (also known as LED high-bay lights), such as those using power of 150 W˜300 W, their luminous flux can reach about 20000 lumens˜45000 lumens. In this case, a heat sink must dissipate heat from an LED lamp with 20000˜45000 lumens under its weight limit.
Currently mainly available heat dissipating components for LED lamps are fans, heat pipes, heat sinks or their combination to dissipate heat of an LED lamp by thermal conduction, convection and/or radiation. Under a condition of merely adopting passive heat dissipation (without a fan), an overall effect of heat dissipation depends upon thermal conductivity and heat dissipation area of material of the heat sink. Under a condition of the same thermal conductivity, heat sinks merely rely on both convection and radiation to dissipate heat regardless of types thereof. Heat dissipating ability of these two types of heat sinks is in proportion to heat dissipating area thereof. Thus, under a precondition of a weight limit for a heat sink, how to improve efficiency of heat dissipation of a heat sink is an important way to enhance quality of LED lamps and reduce cost of LED lamps.
A currently available LED lamp generally includes a light source, a heat sink, a power source, a lamp shell and a lamp cover. The light source is fastened onto the heat sink. The power source is disposed in the lamp shell. The lamp shell connects to the heat sink. The lamp shell includes a head for connecting a lamp socket. Currently available LED lamps have the following drawbacks:
1. Concerns with designs of heat sinks:
Under a condition of merely adopting a manner of passive heat dissipation within the weight limit of a heat sink, a problem of heat dissipation of LEDs of some high-power LED lamps may exist so that heat from working LEDs cannot be dissipated timely. Life of these LEDs will be affected after long term use. As an example, a heat sink may include fins, but a relative positional relationship between the fins and LEDs may be arranged so as to make a heat conduction path of the heat from the LEDs to the fins too long to dissipate heat of LEDs fast enough.
Further, certain convection designs between fins of a heat sink may be impractical or ineffective. For example, Chinese patent No. 2047174890 teaches a fanless LED projection light. There is no convection from bottom to top between wing sheets of '489's heat sink so that heat in the air cannot be timely dissipated after heat in the wing sheets has been radiated to the air. As a result, the temperature of air around the wing sheets increases. An important factor of affecting thermal radiation of the wing sheets is a temperature difference between the wing sheets and air therearound. Accordingly, a raise in air temperature would affect thermal radiation of the wing sheets.
Moreover, certain structural designs of fins of a heat sink may be impractical or ineffective. For example, Chinese patent No. 107345628A teaches an LED lamp whose fins in a direction of a height of the LED lamp have the same width. For heat dissipation of an LED lamp, fins near LEDs in a direction of a height of the LED lamp are mainly used for conducting heat of the LEDs to the fins and the fins away from the LEDs are used for dissipating heat to air therearound by thermal convection and radiation. The fins away from the LEDs dissipate heat to air therearound by thermal convection and radiation, so no excessive heat dissipating area is required. However, the design of fins of the LED lamp disclosed by '628 would cause increase of overall weight of the LED lamp without proportioned increase of efficiency of heat dissipation.
In addition to the above issues, fins of a heat sink may still have some structural problems. For example, a high-power LED lamp with a larger size, whose width may be above 150 mm and height may be above 180 mm, should match fins with correspondingly larger length and width. If such fins lack sufficient support, they tend to be skewed in assembling. In addition, an unreasonable design of radial outlines of fins would reduce an effect of heat dissipation and may not properly match a lamp.
2. Concerns with arrangement of power sources:
For some high-power LED lamps, such as power of up to 150 W˜300 W, heat dissipation of their power sources is also important. If heat from a power source of a working LED lamp cannot be dissipated timely, then life of some electronic components will be affected and finally life of a whole lamp will be affected. Usually, there is no effective heat management between a heat sink and a power source in a currently existing LED lamp. This will result in mutual influence between heat of a heat sink and a power source. For example, Chinese patent No. 2031903640 teaches a heat dissipating structure with double-channeled air convection for a lamp. No effective thermal isolation is provided between its fins and a chamber (a part of the chamber is directly formed on the heat sink) receiving a power source or between its light source and the chamber receiving the power source. Heat from the fins and the light source may therefore directly enter the chamber through thermal conduction to affect the power source in the chamber.
Furthermore, certain layouts of electronic components of a power source may cause problems for heat dissipation. For example, laying out heat-generating components (such as resistors, inductors and transformers) together may be disadvantageous to forming of temperature gradients between the heat-generating components and air therearound so as to adversely affect efficiency of heat radiating from the heat-generating components to air. It is noted that when external air is thermally transferred to the power source and no particular design is provided, then bugs and dust tends to be attached on the power source to affect heat dissipation of the power source.
Besides the problem of heat dissipation, high-power LED lighting possesses relatively heavier weight and a higher working temperature, so a requirement of structure of high mechanic strength under a high temperature should be considered. A general high-power LED lighting is assembled by screwing components to connect. Considering a requirement of distance of insulated creepage, a lamp neck above a heat sink usually adopts a plastic material. The most common structure is that a casing of a plastic element is together with a lamp head thread, the lamp head is screwed to the casing and riveting pinholes are added to implement positioning connection. Connection using screws not only requires complicated process in manufacture, but also cost is higher. Thus, mechanic connection of high-power LED lighting is another important issue for these products.
When packing and shipping of LED lamps are involved, a lamp cover of an LED lamp protrudes from a light board. For example, in Chinese patent No. 107345628A, the lamp cover of the LED lamp may touch external objects to cause damage. Therefore, when packing and shipping, the lamp cover needs to be particularly protected to avoid damage resulting from collision. This will increase packing cost.
When considering light emission of LED lamps, usually, under an ideal condition, light from an LED lamp is expected to be projected onto a specific area under the LED lamp to guarantee intensity in this area. However, in fact, a considerably large part of light may be projected to a lateral area to cause waste of light and decrease of output efficiency of light. For example, Chinese patent No. 107345628A discloses a solid state lamp including a solid state light source on a circuit board. A part of the solid state light source is laterally disposed. A lamp is usually used with the light source. A solid state light source which is laterally disposed may use a lamp to reflect its light to project downward. In the process of reflection, there is typically light loss. Thus, efficiency of light emission will be adversely affected.
Furthermore, for circuits, a bias of conventional driving circuits is generated by acquiring voltage division on a mother line. In applications of HID-LED (High intensity Discharge-LED), however, large capacitors are usually used in conventional biasing circuits to avoid excessive power waste. This may cause a situation where the HID-LED cannot be lit up immediately. Typical starting time of general biasing is about 1 second. This can affect convenience of use.